We propose to construct a vector system for studying protein-protein interaction. The proposed vector system will be coupled with rapid cDNA library construction and protein interaction methods. The series of compatible multipurpose vectors proposed will allow: i) construction of high titer libraries ii) directional cloning of cDNAs and protein-encoding genes. iii) efficient screening and selection of interacting protein molecules, and iv) rapid analysis of cloned inserts. An advantage to the proposed vector systems is that protein purification will not be needed in order to clone interacting protein molecules.